In response to tighter guidelines recently imposed by the federal Environmental Protection Agency under the Clean Water Act, controlling pollution, silt and sediment found in storm water runoff and other sources of water is receiving ever-increasing attention at all levels of government, federal, state and local. Federal and state agencies have issued mandates and developed guidelines regarding the prevention of non-point source (storm water caused) pollution that require local governments to act upon or initiate. These mandates affect water runoff from storms and also from other sources on slopes and construction sites. In addition, there are many other laws and regulations in place that restrict how any significant amount of water may be moved or disposed. Such laws and regulations have a significant impact on not only how storm water may be channeled and diverted, but also on, for example, the ways that contractors can dispose of excess or unwanted water from constructions sites. Regulations also exist as to how clean water must be as it is pumped away or “dewatered” from lakes, ponds and water filled trenches, such that undesirable excess silt and particles are not introduced into streams, storm sewers and surrounding property.
Dewatering bags, also known as “dirt bags,” are a common way of filtering or treating dirty water that must be pumped or otherwise moved from one location to another. Such dewatering bags are manufactured and sold commercially by numerous entities, with examples including ACF Environmental of Richmond, Va., and Dandy Products, Inc. of Grove City, Ohio. Dewatering bags generally resemble a large bladder comprised of a permeable filtering membrane, such as a non-woven geotextile fabric, and are typically rectangular in nature, although other shapes may be available. Sizes vary widely according to anticipated fluid flow rates, and range anywhere from about four feet square to about fifteen feet square. An inlet spout extending from one side of the dewatering bag is typically able to accept an inlet hose or pipe up to six inches in diameter. Water may be pumped into the dewatering bag from the desired source through this inlet hose or pipe at rates up to 1500 gallons per minute, depending upon factors such as the size of the bag and the permeability of the membrane. In the event that such high flows are desired, the typical solution is to use an extremely large dewatering bag, such as one that is fifteen feet by fifteen feet. Use of such large bags can be cumbersome and include added cost, however, and such use also tends to subject a much greater load on any surface upon which the bag rests, which may be detrimental should such a surface comprise grass or ground susceptible to erosion. In addition, use of large dewatering bags forces a user to disperse of large outflows of water in one large localized area, and in some cases a sufficiently large area or surface may not be convenient or available. Accordingly, improved methods and systems for dewatering at large flow rates are desired.
Referring now to FIG. 1, a top perspective view of a prior art dewatering bag in operation is illustrated. In a typical application, a dewatering bag 10 is laid flat wherever pumped water is desired to be dispersed, and is ideally placed atop a bed of vegetation, straw, gravel or any other aggregate base 20 such that filtration and permeation through the bottom of the bag may be maximized. Dewatering bags may be used on either sloped or level surfaces as needed, and each type of surface has its own separate advantages. Once a source hose or pipe 30 is inserted into an inlet spout 11, a tie down strap or rope 12 firmly wraps around the inlet spout to secure it in place and prevent gross leakage of unfiltered water. Dirty water is then pumped into the dewatering bag, and the bag tends to balloon up in size as it fills. At the same time that water is being pumped into the bag, water 13 is constantly seeping out of or otherwise escaping the bag through the permeable material around all sides, top and bottom of the bag. Because the dewatering bag is made from a fabric or other type of permeable membrane 14, however, much of the sediment, silt and suspended solids in the incoming water are retained inside the bag. Of course, a very fine filtration level of the permeable membrane would result in a reduced aggregate flow capacity out of all sides of the bag, such that under most reasonable output flows, a good amount of sediment and fine solids do nevertheless pass through the membrane with the outgoing water. Because many laws and regulations only require that pumped water be treated or clarified in some minimal way, however, a mere reduction in the murkiness of the water is sufficient for most dewatering bag applications. As regulations tighten or various applications require a higher standard of treatment for dirty or murky water, better methods and systems for dewatering at reasonably high flow rates may thus be needed.
One of the drawbacks to existing dewatering bags is that such bags are typically disposable and are designed to be used only once before being thrown away. In addition, silt, sedimentation and mud build up inside a dewatering bag rapidly during regular use, such that these solids begin to line the permeable membrane from the inside and otherwise clog the bag. Such buildup reduces the effective outflow capacity of the bag in short order to the point where the disposable bag is no longer useful, and the average lifespan of most dewatering bags is quite short. In fact, many applications will require numerous dewatering bags to pump away a desired body of water, with each used up dewatering bag being disposed of or thrown away as it fills with mud and silt. Not only can use of multiple disposable bags be costly, but such use may also be harmful to the environment in some cases where bags must be thrown away. Accordingly, better methods and systems for recycling and reusing dewatering bags are desired.
Chitosan is a well-known material that is derived from a naturally occurring substance called chitin, which is a polysaccharide found in the exoskeleton of shellfish such as shrimp, lobster, and or crabs. While chitosan is has recently gained popularity as a dietary supplement, its inherent ability to generate small electrical charges has also provided benefits in the processing of contaminated items, such as wastewater. In turbid or polluted water, the electrical charges given off by chitosan react with the small electrical charges in pollution, fine silt and sediment particles, such that many of these tiny bits of contamination and silt coagulate together into larger chunks. These larger coagulated chunks of particles can then be filtered more easily from the fluid and are also more prone to settle to the bottom of the fluid body via gravity. An appropriate application of chitosan can render a body of muddy water as fairly clear in a short period of time. While chitosan and chitin have been previously used to some extent in the treatment of wastewater, their use has yet to reach the field of storm water runoff or other dirty water coming under other concerns of the Clean Water Act, with its accompanying objective to filter or clarify such water. Accordingly, more effective devices and systems are desired for filtering or clarifying polluted or dirty water using chitosan technologies.